This invention relates generally to a system and method for providing communication channels from centrally located cellular basestations to remotely located cells in a way that can significantly reduce the required number of channels needed to serve the remote communication traffic.
In a typical cellular communication system, a geographic area is divided into coverage areas called cells. In a cell, cellular traffic is provided by a cellular basestation. The basestation provides radio coverage for a cell through its front end. This basestation""s radio coverage establishes RF communication links to and from mobiles users. These communication links are referred to as traffic channels. In this arrangement, the number of radio channels allocated to each cell is fixed. Since each cell must be served by enough channels to meet the peak demand capacity with a specified grade of service or a probability of call blocking, the total number of radio channels required in the system can be quite high. Therefore, the costs can also be high. Also in this arrangement, the overall system efficiency is poor because the demands in certain cells sometimes exceed its peak traffic capacity, causing capacity shortages in some areas and excesses in others. The overall system inefficiency of this nature is common in other communication areas such as data communications, radio coverage, and cellular communication systems. Efforts have been made to solve this problem. In the study of data networks much attention has been focused on providing algorithms that direct data optimally through network to maximize the network""s capacity. Typical algorithms will divert data streams from overload network links to other less utilized links to increase the system throughput. One example of such algorithm is given in an article entitled xe2x80x9cAdaptive Capacity Management of Virtual Path Networks,xe2x80x9d by U. Mocci et al., IEEE 1996, page 750-754. This article gives a scheme for allocating physical link capacity among various virtual data path traversing the link. This scheme only improves the efficiency of the network by the virtual paths. The physical links remain fixed. Therefore, the costs of the pre-determined physical links in a virtual path network are still the same.
There also exist inventions related to various aspects of cellular coverage and capacity. Salmela, U.S. Pat. No. 5,805,996, dated Sep. 8, 1998, proposes a method for enhancing coverage to specific areas within a cell by adjusting the direction of one or more antennas. In this case, traffic channels are steered by physically pointing the antennas from neighboring cells into cells with high capacity demand. Hence, additional capacity is provided by neighboring basestations. The system still needs many basestations at the cell""s  sites. Thus the costs are high and it is not easy to maintain such dispersed basestations.
In Rui, U.S. Pat. No. 5,890,067, dated Mar. 30, 1999, a method for using narrow beam antennas to follow mobile cellular users is disclosed. Different antennas beam widths are used to provide coverage zones for low, medium, and high density traffic areas. This concept is similar to smart antenna systems in which phase-array antenna beams are used to direct coverage to specific mobiles or traffic areas. As mentioned in the above invention, in Salmela""s invention, the improvement is limited because capacity is steered locally within a single cell or sector.
In Gilmore, U.S. Pat. No. 5,861,844, dated Jan. 19, 1999, a combine array is used to steer radio coverage from functioning cells or sectors in to a cell or sector wherein a RF transceiver has failed. In this method, RF transceivers from neighboring cells can temporarily provide coverage into those cells with failed transceiver until the failed transceiver can be replaced. Thus this method only improves reliability of coverage but not efficiency and costs.
In Doren, U.S. Pat. No. 5,854,986, dated Dec. 29, 1998, a method for coupling a plurality of transceivers to low power distributed antennas is presented. The purpose is to provide confined coverage in areas with high capacity demands or, alternatively, low capacity coverage holes. Because the coupling is pre-determined statically during installation, this method does not offer a solution to time varying demands.
Finally, Labedz, U.S. Pat. No. 5,852,778, dated Dec. 22, 1998, proposes a method for allowing nearby Code Division Multiple Access (CDMA) cells to expand into coverage area holes caused by a malfunction transmitter. This method is not based on traffic considerations and does not use any RF routing hardware to affect the change in coverage. Again, this method of CDMA cell expansion does not solve any efficiency problem nor does it solve any dynamic coverage demand.
The main objective of this invention is to achieve a system sensitive to traffic demands, and capable of switching traffic channels from one cell to another. Based on the information from the traffic demands, the invented system physically assigns channels to cells that have high traffic by borrowing channels from cells that have low traffic demand. In this system, the number of traffic channels in each cell is not fixed anymore. Given cell""s peak times do not overlap, the invented system reduces the total number of traffic channels needed to serve the system-wide traffic. Thus the system reduces the required capacity, cuts costs, and dynamically improves overall system efficiency.
Not only does the invented system solve the efficiency, costs, and capacity problems, it is physically different from existing systems.
The key difference between the data network capacity maximizing strategies and the present inventions are that (1) the former treats digital packet-switched data whereas this invention treats RF signals, (2) the former deals with a network with fixed communication links whereas this invention dynamically moves physical links (or traffic channels) among cells, and (3) the optimization method of this invention is unique.
In other systems, there is no routing of traffic channels, no centralization of channel resources, and no attempt to determine optimal allocations of traffic channels.
An Adaptive Capacity Management System receives information and instructions from a controller and assigns channels to remote cells in such that the total number of channels needed is minimal at a given grade of service (GoS). The system comprises one or more centrally located basestations, a capacity management controller, a router, RF transport means, and RF transceivers. In this arrangement, the basestations provide RF channels and the radio transceivers are located in the cell sites (far away from the basestations) to provide RF coverage. The RF transceivers communicate with the centrally located basestations through RE transport means. If the capacity demands of the system shift from cell to cell over time then the intelligent capacity management system described herein can divert traffic channels to where they are needed. As a result, the present invention substantially reduces the total number of radio channels required to serve the system-wide traffic. Furthermore, in this arrangement, it is easy to operate and maintain the one or more central basestations because they are centrally located.
Four algorithms are invented to use in the Adaptive Capacity Management System to allocate channels to cells. Each algorithm uses a specific metric to minimize the number of channels required to serve the system-wide traffic. These metrics are the worst-case blocking metric, the system blocking metric, the weighted average blocking metric, and the expected number of calls metric.